Prep the avocados. Cut the avocados in half, remove the pits, and scoop the flesh into a blender or food processor.
Make sure there are no fibrous bits.
Add the base ingredients. Add cocoa powder, maple syrup or honey, vanilla, and salt. Start with the lower amount of sweetener—you can add more later.
Blend with milk. Add 2 tablespoons of milk and blend until completely smooth, pausing to scrape down the sides. If the mixture is too thick, add another tablespoon of milk.
Taste and adjust. Check sweetness and chocolate intensity.
Add more sweetener or cocoa powder if needed. If you want a richer flavor, blend in melted dark chocolate or a touch of espresso powder.
Chill to set. Spoon the mousse into small bowls or ramekins. Cover and refrigerate for at least 30–60 minutes so the flavors meld and the texture firms up.
Garnish and serve. Top with whipped cream, berries, shaved chocolate, or nuts.
Serve chilled.